Polarization of an antenna refers to the orientation of an electric field of its radio wave with respect to the earth's surface and is determined by the physical structure of the antenna and by its orientation. Thus, a simple straight wire antenna will have one polarization when mounted vertically, and a different polarization when mounted horizontally.
Polarization is largely predictable from antenna construction. For radio antennas, polarization corresponds to the orientation of the radiating element in an antenna. For a linearly polarized antenna, a vertically positioned antenna will result in vertical polarization. Similarly a horizontally positioned antenna will result in horizontal polarization.
In practice, it is preferable that the orientation of linearly polarized antennas on a transmitter are matched with the orientation of the linearly polarized antennas on a receiver, or else the strength of a signal received at the receiver will be reduced. That is, vertically polarized antennas on a transmitting device are preferably used with vertically polarized antennas on a receiving device and horizontally polarized antennas on a transmitting device are preferably used with horizontally polarized antennas on a receiving device. Intermediate matchings between transmitter antenna and receiver antenna will result in a loss of some received signal strength, but not as much as would result in the case of a complete mismatch between antenna polarizations.
The most common and cost effective method for providing circular coverage area around a base-station antenna is to install an omni-directional antenna pointed upward, perpendicular to the earth. This forces vertical polarization and provides a pattern that is omni-directional in azimuth. Such an antenna position is used in many radio communication schemes such as wireless phone networks, mobile ultra high frequency (UHF) radio such as Citizen's Band (CB) radio, Wi-Fi™ and the like. If the same antenna is mounted parallel to the earth then it will yield horizontal polarization. As a result, the pattern is no longer omni-directional but a “figure 8”. That is, for example, if the tip of the antenna is at 0°, then you will have maximum radiation 90° and 270°, but little radiation at 0° and 180° deg. If there is a need to provide omni-directional coverage with horizontal polarization then the most common method is to use three sector antennas, each designed for horizontal polarization. As a result, it is more expensive and complex to implement an omni-directional horizontally polarized antenna because there are three antennas, a three-way splitter, and three more cables.
Thus, many radio transceivers such as base-stations, for example, are configured with vertically polarized antennas. Accordingly, it is preferable to provide vertically polarized antennas in the transmitting devices in communication with the base-stations. However, due to size limitations, antennas in some mobile communication devices are configured in a horizontal position and, thus, are horizontally polarized. This mismatch results in a loss of signal strength between the mobile communication device and the base-station.
In order to overcome this problem, base-stations or the like can be configured to have horizontally polarized antennas in order to match the horizontally polarized antennas in the mobile communication devices. Such a solution is easiest to implement when designing a network infrastructure from scratch. However, if the mobile communication device is to be used in an existing infrastructure, it is a deterrent to suggest that the existing network infrastructure be overhauled in order to use the mobile communication device efficiently. Further, it is likely that the mobile communication device will be used along with a plurality of different devices, potentially having differently polarized antennas, exacerbating the problem. Yet further, as described above, it is more expensive to provide a base-station having an omni-directional antenna that is horizontally polarized.
Therefore it is an object of the present invention to obviate or mitigate at least one of the above mentioned disadvantages.